Our major hypothesis is that insulin and cellular ion transport are major determinants of the relationship among obesity, diabetes and hypertension, three major cardiovascular risk factors. Positive interrelationships have been observed among blood pressure, obesity, plasma insulin, plasma lipids, sodium-lithium countertransport, sodium-hydrogen exchange and renal proximal tubule sodium reabsorption. This study will examine the hypotheses that: 1) part of the relationship between obesity and blood pressure is due to insulin effects and/or lipid effects on ion transport; 2) the relationship between ion transport and blood pressure, whether dependent or independent of obesity, insulin, and lipids, is related to an abnormality of Na-H exchange, a cation exchange for which the observed increase in Na-Li countertransport is a marker; and 3) increased blood pressure is related to the alteration of intracellular pH and/or calcium concentration. We propose a cross-sectional study of normotensive and untreated hypertensive, white subjects, aged 35-55, stratified by desirable weight + 10%; 11 to 30% over desirable weight; 30% over desirable weight; by blood pressure. 80, 80-89, 90-99mmHg. Two hundred and seventy subjects will be recruited, 15 male and 15 female in each of nine substrata. In addition, 60 untreated non-insulin dependent diabetics will be recruited, Blood pressure, height, weight, waist, hip, skinfolds, fasting plasma insulin, glucose, lipids, creatinine, maximal rates of red blood cell Na- Li countertransport, and platelet Na-H exchange, pH, and Ca concentration will be measured. Strength and independence of interrelationships among these continuous variables will be measured by Pearson correlations, partial correlations, and multiple regression within each stratum and, if appropriate, over all strata, This study should increase our understanding of the role that insulin, lipids, body weight and ion transports play in the etiology of hypertension.